(i) Field of the Invention
The present invention relates to a resin composition. More specifically, the present invention relates to an olefin resin composition having a surface suitable for the application of coating, bonding and printing.
(ii) Description of the Related Art
In order to wash off and remove hand dirt, machine oil and the like adhered to the surface of a resin molding, prior to the coating of the surface thereof, vapor washing is generally carried out by employing halogen containing organic solvents.
Further, as olefin resins do not contain polar groups in the structure thereof and additionally because such resins have a higher degree of crystallinity, they show extremely poor adhesive property for paints, adhesives, printing inks and the like; in other words, the coating, adhesive and printing properties thereof are insufficient. Therefore, the surface is primarily coated with primers or is subjected to plasma treatment, whereby the surface is modified to improve the adhesive property. Thereafter, paints and adhesives are applied thereto or printing inks are used thereon for printing.
However, such methods have conventionally involved the following problems.
That is, concern has been shown about the vapor washing process using halogen containing organic solvents in the coating and adhesion of resin moldings, because the atmospheric diffusion of halogen containing organic solvents may cause possible damage to the ozone layer. From the standpoint of protecting the global environment, an early switch to alternate methods has been sought.
Also, in accordance with the primer coating method, expensive primer must be used and it involves a great number of processes. Therefore, this method has defects in that it is costly and deteriorates the working environment because of the requirement to evaporate the primer solvents which might also lead to the risk of fire, a safety problem.
On the other hand, the plasma treatment process requires a costly apparatus because it needs a high degree of vacuum and also inevitably involves an escalation of cost because of the batch system. Furthermore, the surface after the plasma treatment is instable and decreases the adhesive properties thereof for coatings, adhesives and printing inks when in contact with foreign matter. Accordingly, the adhesion strength may sometimes vary, which is very inconvenient for the handling thereof. If such primer coating or plasma treatment processes can be omitted, simplification of the coating process, improvement of working environment and cost reduction should be achievable and therefore a great deal of research has been carried out towards solving these problems.
However, this objective has not yet been achieved and currently, such primer coating and plasma treatment process cannot be omitted in the case of olefin resin materials. In many cases, coating, bonding and printing are effected after such processes.
There are reports describing that the adhesive property for coatings, adhesives, printing inks and the like are improved by compounding a copolymer resin containing non-conjugated dienes with an olefin resin, thereby effecting specific surface treatment. For example, a method of surface treatment with cationic halogen compounds (Japanese Patent Laid-Open No. 63-64460), a method of surface treatment with an aqueous saturated potassium permanganate solution acidified with sulfuric acid and an aqueous 3% sodium hydrogensulfite solution acidified with sulfuric acid (Japanese Patent Laid-Open No. 57-44639), a method of surface treatment with an oxidant (Japanese Patent Laid-Open No. 57-59934), a method of surface treatment with ozone (Japanese Patent Laid-Open No. 61-197640) and the like are known.
There are also known methods using a specific coating or coated compositions or the like illustrated for example by a method for coating olefin resin moldings using a radical-polymerization cured-type coating (Japanese Patent Laid-Open Nos. 57-38825 and 57-59933), a method using a resin-coated composition having a hydrazine group (Japanese Patent Publication No. 3-22896), and the like.
However, these methods have disadvantages in that their application is extremely limited to a very narrow field because they use certain chemical reagents, they require environmental counter measure to counter the toxicity of sulfuric acid, their complex procedures, they are very inconvenient to handle, and they are limited to certain types of paints, coated compositions and the like. It has also been proposed to impart excellent Coating and paint adhesive properties to a polyolefin resin compound, by adding a phosphate compound having a specific structure to the polyolefin resin (Japanese Patent Laid-Open No. 3-26537). However, such paint adhesive properties cannot be imparted to the resin if the process of surface modification such as primer coating or plasma treatment process is omitted.
In order to modify adhesive properties with metal, glass and the like, a proposal has been presented such that a hydrocarbon polymer having at least one hydroxyl group is compounded with a polyolefin (Japanese Patent Laid-Open No. 53-123452). However, the publication only contains an embodiment disclosing ethylene/propylene rubber as the polyolefin.
EP-A 0429236 discloses that a coated resin molding comprising a molding composed of a resin composition comprising a substrate resin comprising at least one propylene polymer selected from the group consisting of propylene/ethylene block copolymers and propylene/ethylene random copolymers and an elastomer, at least one member selected from the group consisting of (A) a 1,3-diene polymer having at least one terminal hydroxyl group or a hydrogenation product thereof, (B) a copolymer of ethylene with an unsaturated compound containing a carboxyl group (including an acid anhydride group) and (C) a copolymer of ethylene with an unsaturated compound containing a hydroxyl group, and a coating formed directly on the surface of said molded body.
According to the proposal immediately described above, however, the molding should be washed preliminarily with trichloroethane and the like in order to produce a resin molding with satisfactory paint adhesive property.